93 Jeep Grand Cherokee Cranks, But No Start

rifleman did pass the time by typing:
> Ok, here's the current situation...

> I know the system is running checks when the light is on, and
> sometimes something isn't letting it come on, ergo no checks and
> nofuel priming. Anyone ever see this before?

Delays like that sound like thermal or leak current. Dirty connectors
can cause similar problems.

Did you pull trouble codes when the lamp didn't light?

> Last note.. sometimes, and only sometimes, I hear a clicking when I
> turn the key to RUN. It sounds like a circuit switching on/off. During
> all this testing, I did not hear it once.

There are quite a few relays in the vehicle, apart from a smattering of
relays under the dash, the primary center is located in the glovebox.
It holds relays for Interior lights, power door locks, horn, power antenna,
heated rear window, and the security alarm relay that flashes the
lights and beeps the horn.

I'm running out of ideas, short of having a local dealer put a scantool
on the system and run a full diagnosis. Most sensor faults are stored
but on the 93 there is limited testing ability.

Failure to start can be the camshaft position sensor or the crankshaft
position sensor. It can also be the coil. Anything that causes a no-start
after a couple of engine cranks will turn off the ASD relay and remove power
to the ignition coil. IF you have a test lamp, backprobe the coil wire that
runs to the relay center. The lamp should light when you turn the key ON
and stay lit while the engine cranks. It will go out if the engine doesn't start
after a couple of revs. If it never comes on then there is another issue.
(dead sensor/ECU fault) but most of those should be in the diagnositc codes.

One thing you might try though is to clean the ECU connectors.
(disconnect the battery + before doing this)

You will have to remove the overflow bottle to gain access to the ECU.
in the center of the large connector is a bolt, this has to come out.
Turn it out, wiggle the connector, turn it out, wiggle the conector..etc.
Don't use this bolt to force the connector on or off, it will crack the ECU!
take the bolts out that hold the ECU to the firewall then rinse out the ecu
with a plastic safe contact cleaner. Do the same to the connector. A bit
of sandpaper on a stick can be used to clean off some of the connectors.
Put some dilectric grease (sparkplug boot grease) on the connector before
you put it back.

Again, when you put the ECU back. Don't crank on the bolts that hold it down
and don't use the connector bolt to suck the connector on. Press, tighen, press
tighten, etc.

Also, when cleaning the connector, don't forget to clean the wire side, that's
where 90% of the buildup accumulates.


--
DougW

Or a bad motor.
God Bless America, Bill O|||||||O
http://www.billhughes.com/


DougW wrote:
>
>
> Delays like that sound like thermal or leak current. Dirty connectors
> can cause similar problems.
>
> Did you pull trouble codes when the lamp didn't light?
>
> There are quite a few relays in the vehicle, apart from a smattering of
> relays under the dash, the primary center is located in the glovebox.
> It holds relays for Interior lights, power door locks, horn, power antenna,
> heated rear window, and the security alarm relay that flashes the
> lights and beeps the horn.
>
> I'm running out of ideas, short of having a local dealer put a scantool
> on the system and run a full diagnosis. Most sensor faults are stored
> but on the 93 there is limited testing ability.
>
> Failure to start can be the camshaft position sensor or the crankshaft
> position sensor. It can also be the coil. Anything that causes a no-start
> after a couple of engine cranks will turn off the ASD relay and remove power
> to the ignition coil. IF you have a test lamp, backprobe the coil wire that
> runs to the relay center. The lamp should light when you turn the key ON
> and stay lit while the engine cranks. It will go out if the engine doesn't start
> after a couple of revs. If it never comes on then there is another issue.
> (dead sensor/ECU fault) but most of those should be in the diagnositc codes.
>
> One thing you might try though is to clean the ECU connectors.
> (disconnect the battery + before doing this)
>
> You will have to remove the overflow bottle to gain access to the ECU.
> in the center of the large connector is a bolt, this has to come out.
> Turn it out, wiggle the connector, turn it out, wiggle the conector..etc.
> Don't use this bolt to force the connector on or off, it will crack the ECU!
> take the bolts out that hold the ECU to the firewall then rinse out the ecu
> with a plastic safe contact cleaner. Do the same to the connector. A bit
> of sandpaper on a stick can be used to clean off some of the connectors.
> Put some dilectric grease (sparkplug boot grease) on the connector before
> you put it back.
>
> Again, when you put the ECU back. Don't crank on the bolts that hold it down
> and don't use the connector bolt to suck the connector on. Press, tighen, press
> tighten, etc.
>
> Also, when cleaning the connector, don't forget to clean the wire side, that's
> where 90% of the buildup accumulates.
>
> --
> DougW

>"DougW" did pass the time by typing:
>Delays like that sound like thermal or leak current. Dirty connectors
>can cause similar problems.

I've been pulling and cleaning anything I find as I go along and no
change.

>Did you pull trouble codes when the lamp didn't light?

There are no trouble codes. The only thing the system is holding atm
is the battery has been disconnected because it was during tests.

>There are quite a few relays in the vehicle, apart from a smattering of
>relays under the dash, the primary center is located in the glovebox.
>It holds relays for Interior lights, power door locks, horn, power antenna,
>heated rear window, and the security alarm relay that flashes the
>lights and beeps the horn.

I'm not certain the clicking I occasionally here is related to this
problem or not, but since I'm not positive of whats behind the
glove/dash, I thought it a possible important note. I know the fuse
box has four circuit breakers in it and that one is for the alarm.
Since I can hear the rear window defrost relay "click" when I turn it
on and off, I was hoping the alarm circuit might do the same, but it's
the only one and it appears to be working.

>I'm running out of ideas, short of having a local dealer put a scantool
>on the system and run a full diagnosis. Most sensor faults are stored
>but on the 93 there is limited testing ability.

I've talked to a few people and the concensus is this isn't a senor
problem.I'm just hoping it's not the ECM.

>Failure to start can be the camshaft position sensor or the crankshaft
>position sensor. It can also be the coil. Anything that causes a no-start
>after a couple of engine cranks will turn off the ASD relay and remove power
>to the ignition coil. IF you have a test lamp, backprobe the coil wire that
>runs to the relay center. The lamp should light when you turn the key ON
>and stay lit while the engine cranks. It will go out if the engine doesn't start
>after a couple of revs. If it never comes on then there is another issue.
>(dead sensor/ECU fault) but most of those should be in the diagnositc codes.

But would any of these cause the dash "Check Engine" light to fail to
light or delay it to light?

>One thing you might try though is to clean the ECU connectors.
>(disconnect the battery + before doing this)
>
>You will have to remove the overflow bottle to gain access to the ECU.
>in the center of the large connector is a bolt, this has to come out.
>Turn it out, wiggle the connector, turn it out, wiggle the conector..etc.
>Don't use this bolt to force the connector on or off, it will crack the ECU!
>take the bolts out that hold the ECU to the firewall then rinse out the ecu
>with a plastic safe contact cleaner. Do the same to the connector. A bit
>of sandpaper on a stick can be used to clean off some of the connectors.
>Put some dilectric grease (sparkplug boot grease) on the connector before
>you put it back.
>
>Again, when you put the ECU back. Don't crank on the bolts that hold it down
>and don't use the connector bolt to suck the connector on. Press, tighen, press
>tighten, etc.
>
>Also, when cleaning the connector, don't forget to clean the wire side, that's
>where 90% of the buildup accumulates.

Is the ECU the only thing that sets the "Check Engine" on and into
it's diagnostic mode? I was hoping for some more light on these areas.

>On Thu, 23 Feb 2006 18:47:55 -0800, L.W.(ßill) Hughes III wrote:
> Or a bad motor.
> God Bless America, Bill O|||||||O
http://www.billhughes.com/

Um, I think the fact that it consistantly starts when the "Check
Engine" light comes on on the dashboard indicates this is not a
mechanical problem. The engine is sound, cept for an oil change, and
no point in doing that until I can resolve this weird issue.

sounds like an intermittant connection.

could be a ground or a wire or a connector.

when the light is out, start wiggling wires.

Casper did pass the time by typing:

> Is the ECU the only thing that sets the "Check Engine" on and into
> it's diagnostic mode? I was hoping for some more light on these areas.

The ECU (engine brain) is what does all the testing and lights the Check Engine
light.

Here is a few things that might help you understand how things hook up.

SBECii (the computer) pdf file.
http://www.revbeergoggles.com/temp/sbecii.pdf

service book
http://www.revbeergoggles.com/temp
You want zj-13.jpg to zj-18.jpg

I had a one-page diagram for the ECU and sensors, but I can't find
it right now. :/

--
DougW

Have someone kick the tank and see if that speeds up your process.
God Bless America, Bill O|||||||O
http://www.billhughes.com/

wrote:
>
> Um, I think the fact that it consistantly starts when the "Check
> Engine" light comes on on the dashboard indicates this is not a
> mechanical problem. The engine is sound, cept for an oil change, and
> no point in doing that until I can resolve this weird issue.

I am back a page still, or want to be....

First off you say there is a failure issue or fatal error with the
alarm. It does 'not' work because you cannot program the second key and
the idiot light is flashing failure at you or not flashing when it
should which is a failure. Something has to be 'broken' in that
situation.

Then you said you have power at the fuel pump relay but no power back at
the fuel pump.

Now you say the key sometime turns on everything properly, but most
times doesn't.

I think these are related.

I would be running a booster cable from the negative battery post to
something metal on the firewall to see what happens just because I live
in the rust belt and see too many 'rotted where you can't see them'
connections.

Then I would be trying to find out if I could bypass the alarm and
security key.

Next I would be physically tracing the power from the fuel pump relay to
see what is between that and the pump itself. I would just take a wild
guess and figure the alarm has a cut off relay in there.

Could it be a bad ignition switch causing everything?

Or could the $tealer have screwed the alarm setting when they failed to
program the second key?

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
Canadian Off Road Trips Photos: Non members can still view!
Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
(More Off Road album links at bottom of the view page)

wrote:
>
> Ok, here's the current situation...
>
> Tested all the relays and engine compartment fuse/relay box and they
> are all fine. Checked the interior fuse panel and all is fine.
> Everything in these places is getting voltage.
>
> Here is something we (my good neighbor and I) noticed during this
> testing and starting attempts...
>
> If you turn the ignition to the RUN position, four dash lights should
> come on. 1) ABS, 2) Check Engine, 3)Airbag and 4) Seatbelt.
>
> If you turn the key to RUN, and the "Check Engine" light comes on, the
> jeep will start. If the "Check Engine" light does not come on, the
> jeep will NOT start. If you put the key in the RUN position and the
> "check engine" light does not come on, AND you leave the key in the
> RUN position, eventually the "Check Engine" light comes on and the
> jeep starts. Every time the "Check Engine" light comes on, you can
> hear the fuel pump prime and start the jeep, usually on the first try.
>
> We repeated this pattern for a good 30-60 minutes, giving different
> time intervals inbetween because sometimes the dash lights all come on
> as they should on the first trr, and we wanted to make sure it wasn't
> initial luck. We confirmed there is a definite pattern.
>
> On the very last attempt, it took longer for the light to come on.. at
> least another 20 seconds than all the other previous attempts, AND
> when the "Check Engine" light came on, so did the Security light. The
> Security light remains on for about 3-5 seconds and then went off.
>
> I know the system is running checks when the light is on, and
> sometimes something isn't letting it come on, ergo no checks and
> nofuel priming. Anyone ever see this before?
>
> Last note.. sometimes, and only sometimes, I hear a clicking when I
> turn the key to RUN. It sounds like a circuit switching on/off. During
> all this testing, I did not hear it once.
>
> >On Fri, 17 Feb 2006 16:54:11 -0600, "DougW" wrote:
> >Let's go over the basics then.
> >
> >From the front of the vehicle, remove the fuel pump relay
> >Looking into the hole:
> >
> > 7
> > |
> >
> >6| -8- |10
> >
> > -9-
> >
> >With the ignition on, hole 7 should
> >have 12V from the power center fuses 3(20A) and 15(30A)
> >(same location as the relays)
> >Also check fuse2(20A), the ASD power fuse.
> >
> >Hole 6 should also have 12V, if not check fuse 6(15A)
> >
> >Hole 9 feeds the pump and the heated O2 sensor
> >(If you found blown fuses take a look at the O2 sensor
> >and follow the wire back along the engine to where a clip
> >holds it to the block, then follow that wire up to another
> >clip up above and forward of the engine mount. sometimes
> >that wire will melt and short out. That short can/will blow
> >fuses.)
> >
> >If all looks good at this point then
> >Jumping pin 9 to pin 7 will turn the pump on.
> >
> >You should be able to hear it or watch the fuel rail
> >pressure jump.

> "DougW" did pass the time by typing:
>
>The ECU (engine brain) is what does all the testing and lights the Check Engine
>light.

I figured as much. I know the ECM is the CPU (or brain) of the Jeep. I
just try to avoid talking about it because it ain't cheap to replace.

>Here is a few things that might help you understand how things hook up.
>
>SBECii (the computer) pdf file.
>http://www.revbeergoggles.com/temp/sbecii.pdf
>
>service book
>http://www.revbeergoggles.com/temp
>You want zj-13.jpg to zj-18.jpg
>
>I had a one-page diagram for the ECU and sensors, but I can't find
>it right now. :/

I have a few books here that contain a number of wiring diagrams, but
yours are definitely easier than thumbing thru the manuals.

Thanks for the info. I am going to do a more testing this weekend.

Couple more questions...

Should the fuel pressure be exactly 31psi? When we tested my
neighbor's 95' GC Laredo, his was about 20-21Psi. We expected 30, but
it only went up after starting, and then to about 40-41Psi.

He replaced his ECM last summer because he thought the tranny might be
getting improper signals. As it turned out, one of the tranny
connections had some broken magent pieces that were the culpprit to
his gear switching issues. Once he cleaned that up, it shifts fine.
But it may be that his starting problem began after he replaced the
ECU. He plans on swapping the old ECU back in to test. He offered me
his spare to test but not sure it would work in my 93'GC Limited.
(*Ref Post: 95' GC Laredo - Odd Power/Start Problem)

And your website is cool. :-)

>On Thu, 23 Feb 2006 22:32:54 -0500, Scott in Baltimore wrote:
>sounds like an intermittant connection.
>could be a ground or a wire or a connector.
>when the light is out, start wiggling wires.

Tough to "wiggle" the wires because the light seems to only remain off
for a few seconds.So far, the longest it's been off has been about
30-35 seconds and that only occured once in about 10-15 attempts.
However, I'll wiggle the whole Jeep if it would help. ;-)